A simplified cobalt-lysine method for tracing axon trajectories in the central nervous system of vertebrates.

The cobalt-lysine method for tract tracing in the vertebrate CNS has been shortened and simplified to the following steps: (1) the cobalt-lysine is applied to the nerve or tract being studied; (2) the animal is perfused 1-2 days later by the following sequence of solutions: (a) phosphate-buffered ammonium sulfide, (b) phosphate buffer alone and (c) phosphate-buffered glutaraldehyde; (3) the brain is exposed to the fixative overnight and left in 30% sugar another night; (4) the brain is then frozen and cut on a cryostat; the sections being collected directly on slides; (5) the mounted sections are then put in an intensification solution before dehydration, clearing and coverslipping.